共查询到20条相似文献,搜索用时 265 毫秒
1.
S. Liehr K. Pawelzik 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):555-559
Assuming that financial markets behave similar to random walk processes we derive a trading strategy with variable investment
which is based on the equivalence of the period of bankruptcy risk and the risk to profit ratio. We define a state dependent
predictability measure which can be attributed to the deterministic and stochastic components of the price dynamics. The influence
of predictability variations and especially of short term inefficiency structures on the optimal amount of investment is analyzed
in the given context and a method for adaptation of a trading system to the proposed objective function is presented. Finally
we show the performance of our trading strategy on the DAX and S&P 500 as examples for real world data using different types of prediction models in comparison.
Received 15 September 2000 and Received in final form 2 October 2000 相似文献
2.
G. Schröder T. Knetter M.J. Alava H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):101-105
Random walk arguments and exact numerical computations are used to study one-dimensional random field chains. The ground state
structure is described with absorbing and non-absorbing random walk excursions. At low temperatures, the local magnetization
follows the ground state except at regions where a local random field fluctuation makes thermal excitations easier. This is
explained by the random walk picture, implying that the magnetization lengthscale is a product of the domain size and the
thermal excitation scale.
Received 16 October 2000 and Received in final form 7 June 2001 相似文献
3.
K. Denecker S. Van Assche J. Crombez R. Vander Vennet I. Lemahieu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):481-492
In financial market risk measurement, Value-at-Risk (VaR) techniques have proven to be a very useful and popular tool. Unfortunately,
most VaR estimation models suffer from major drawbacks: the lognormal (Gaussian) modeling of the returns does not take into
account the observed fat tail distribution and the non-stationarity of the financial instruments severely limits the efficiency
of the VaR predictions. In this paper, we present a new approach to VaR estimation which is based on ideas from the field
of information theory and lossless data compression. More specifically, the technique of context modeling is applied to estimate
the VaR by conditioning the probability density function on the present context. Tree-structured vector quantization is applied
to partition the multi-dimensional state space of both macroeconomic and microeconomic priors into an increasing but limited
number of context classes. Each class can be interpreted as a state of aggregation with its own statistical and dynamic behavior,
or as a random walk with its own drift and step size. Results on the US S&P500 index, obtained using several evaluation methods,
show the strong potential of this approach and prove that it can be applied successfully for, amongst other useful applications,
VaR and volatility prediction. The October 1997 crash is indicated in time.
Received 2 September 2000 and Received in final form 12 October 2000 相似文献
4.
V.I. Yukalov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):609-617
A novel approach to analyzing time series generated by complex systems, such as markets, is presented. The basic idea of the
approach is the Law of Self-Similar Evolution, according to which any complex system develops self-similarly. There always exist some internal laws governing the evolution
of a system, say of a market, so that each of such systems possesses its own character regulating its behaviour. The problem
is how to discover these hidden internal laws defining the system character. This problem can be solved by employing the self-similar approximation theory, which supplies the mathematical foundation for the law of self-similar evolution. In this report, the theoretical basis
of the new approach to analyzing time series is formulated, with an accurate explanation of its principal points.
Received 15 August 2000 相似文献
5.
B.K. Nikolić V.Z. Cerovski 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):227-238
We report on the comprehensive numerical study of the fluctuation and correlation properties of wave functions in three-dimensional
mesoscopic diffusive conductors. Several large sets of nanoscale samples with finite metallic conductance, modeled by an Anderson
model with different strengths of diagonal box disorder, have been generated in order to investigate both small and large
deviations (as well as the connection between them) of the distribution function of eigenstate amplitudes from the universal
prediction of random matrix theory. We find that small, weak localization-type, deviations contain both diffusive contributions
(determined by the bulk and boundary conditions dependent terms) and ballistic ones which are generated by electron dynamics
below the length scale set by the mean free path ℓ. By relating the extracted parameters of the functional form of nonperturbative
deviations (“far tails”) to the exactly calculated transport properties of mesoscopic conductors, we compare our findings
based on the full solution of the Schr?dinger equation to different approximative analytical treatments. We find that statistics
in the far tail can be explained by the exp-log-cube asymptotics (convincingly refuting the log-normal alternative), but with
parameters whose dependence on ℓ is linear and, therefore, expected to be dominated by ballistic effects. It is demonstrated
that both small deviations and far tails depend explicitly on the sample size--the remaining puzzle then is the evolution
of the far tail parameters with the size of the conductor since short-scale physics is supposedly insensitive to the sample
boundaries.
Received 19 August 2002
Published online 19 November 2002 相似文献
6.
R. Metzler 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):249-258
A generalised random walk scheme for random walks in an arbitrary external potential field is investigated. From this concept
which accounts for the symmetry breaking of homogeneity through the external field, a generalised master equation is constructed.
For long-tailed transfer distance or waiting time distributions we show that this generalised master equation is the genesis
of apparently different fractional Fokker-Planck equations discussed in literature. On this basis, we introduce a generalisation
of the Kramers-Moyal expansion for broad jump length distributions that combines multiples of both ordinary and fractional
spatial derivatives. However, it is shown that the nature of the drift term is not changed through the existence of anomalous
transport statistics, and thus to first order, an external potential Φ(x) feeds back on the probability density function W through the classical term ∝/
x
(x)W(x, t), i.e., even for Lévy flights, there exists a linear infinitesimal generator that accounts for the response to an external field.
Received 30 June 2000 and Received in final form 12 November 2000 相似文献
7.
8.
S. Wolfling Y. Kantor 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):569-577
Distribution of loops in a one-dimensional random walk (RW), or, equivalently, neutral segments in a sequence of positive
and negative charges is important for understanding the low energy states of randomly charged polymers. We investigate numerically
and analytically loops in several types of RWs, including RWs with continuous step-length distribution. We show that for long
walks the probability density of the longest loop becomes independent of the details of the walks and definition of the loops.
We investigate crossovers and convergence of probability densities to the limiting behavior, and obtain some of the analytical
properties of the universal probability density.
Received 8 January 1999 相似文献
9.
L. Sabatelli S. Keating J. Dudley P. Richmond 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):273-275
We study waiting time distributions for data representing two completely different financial markets that have dramatically
different characteristics. The first are data for the Irish market during the 19th century over the period 1850 to 1854. A
total of 10 stocks out of a database of 60 are examined. The second database is for Japanese yen currency fluctuations during
the latter part of the 20th century (1989-1992). The Irish stock activity was recorded on a daily basis and activity was characterised
by waiting times that varied from one day to a few months. The Japanese yen data was recorded every minute over 24 hour periods
and the waiting times varied from a minute to a an hour or so. For both data sets, the waiting time distributions exhibit
power law tails. The results for Irish daily data can be easily interpreted using the model of a continuous time random walk
first proposed by Montroll and applied recently to some financial data by Mainardi, Scalas and colleagues. Yen data show a
quite different behaviour. For large waiting times, the Irish data exhibit a cut off; the Yen data exhibit two humps that
could arise as result of major trading centres in the World.
Received 31 December 2001 相似文献
10.
D. O. Odero 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):3-8
The time-dependent treatment of positron-hydrogen scattering for a zero total angular momentum has been presented. The initial
wavefunction of the positron-hydrogen scattering system has been expanded in terms of three dimensional dynamical wave functions
to include all higher angular momenta by solving a set of three coupled differential equations. This wavefunction is then
time evolved using Taylor series expansion of the evolution operator. The excitation probabilities are monitored as the wavefunction
propagates until there is no more change in the probabilities. The positron impact excitation cross-sections extracted from
the final wavefunction are compared with the available results of converged close coupling approach.
Received 23 July 2001 and Received in final form 25 November 2001 相似文献
11.
H. Meyer-Ortmanns T. Reisz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):549-558
Dynamical linked cluster expansions are linked cluster expansions with hopping parameter terms endowed with their own dynamics.
We discuss physical applications to systems with annealed and quenched disorder. Examples are the bond-diluted Ising model
and the Sherrington-Kirkpatrick spin glass. We derive the rules and identify the full set of graphs that contribute to the
series in the quenched case. This way it becomes possible to avoid the vague extrapolation from positive integer n to n = 0, that usually goes along with an application of the replica trick.
Received 13 December 2001
Published online 25 June 2002 相似文献
12.
S. Cocco R. Monasson 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):505-531
The computational complexity of solving random 3-Satisfiability (3-SAT) problems is investigated using statistical physics
concepts and techniques related to phase transitions, growth processes and (real-space) renormalization flows. 3-SAT is a
representative example of hard computational tasks; it consists in knowing whether a set of αN randomly drawn logical constraints involving N Boolean variables can be satisfied altogether or not. Widely used solving procedures, as the Davis-Putnam-Loveland-Logemann
(DPLL) algorithm, perform a systematic search for a solution, through a sequence of trials and errors represented by a search
tree. The size of the search tree accounts for the computational complexity, i.e. the amount of computational efforts, required to achieve resolution. In the present study, we identify, using theory and
numerical experiments, easy (size of the search tree scaling polynomially with N) and hard (exponential scaling) regimes as a function of the ratio α of constraints per variable. The typical complexity
is explicitly calculated in the different regimes, in very good agreement with numerical simulations. Our theoretical approach
is based on the analysis of the growth of the branches in the search tree under the operation of DPLL. On each branch, the
initial 3-SAT problem is dynamically turned into a more generic 2+p-SAT problem, where p and 1 - p are the fractions of constraints involving three and two variables respectively. The growth of each branch is monitored by
the dynamical evolution of α and p and is represented by a trajectory in the static phase diagram of the random 2+p-SAT problem. Depending on whether or not the trajectories cross the boundary between satisfiable and unsatisfiable phases,
single branches or full trees are generated by DPLL, resulting in easy or hard resolutions. Our picture for the origin of
complexity can be applied to other computational problems solved by branch and bound algorithms.
Received 10 March 2001 相似文献
13.
14.
S. Pafka I. Kondor 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):277-280
According to recent findings [#!bouchaud!#,#!stanley!#], empirical covariance matrices deduced from financial return series
contain such a high amount of noise that, apart from a few large eigenvalues and the corresponding eigenvectors, their structure
can essentially be regarded as random. In [#!bouchaud!#], e.g., it is reported that about 94% of the spectrum of these matrices can be fitted by that of a random matrix drawn from an appropriately
chosen ensemble. In view of the fundamental role of covariance matrices in the theory of portfolio optimization as well as
in industry-wide risk management practices, we analyze the possible implications of this effect. Simulation experiments with
matrices having a structure such as described in [#!bouchaud!#,#!stanley!#] lead us to the conclusion that in the context
of the classical portfolio problem (minimizing the portfolio variance under linear constraints) noise has relatively little
effect. To leading order the solutions are determined by the stable, large eigenvalues, and the displacement of the solution
(measured in variance) due to noise is rather small: depending on the size of the portfolio and on the length of the time
series, it is of the order of 5 to 15%. The picture is completely different, however, if we attempt to minimize the variance
under non-linear constraints, like those that arise e.g. in the problem of margin accounts or in international capital adequacy regulation. In these problems the presence of noise
leads to a serious instability and a high degree of degeneracy of the solutions.
Received 31 December 2001 相似文献
15.
M. Bauer O. Golinelli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):339-352
We study both numerically and analytically what happens to a random graph of average connectivity α when its leaves and their
neighbors are removed iteratively up to the point when no leaf remains. The remnant is made of isolated vertices plus an induced
subgraph we call the core. In the thermodynamic limit of an infinite random graph, we compute analytically the dynamics of leaf removal, the number
of isolated vertices and the number of vertices and edges in the core. We show that a second order phase transition occurs
at α = e = 2.718 ... : below the transition, the core is small but above the transition, it occupies a finite fraction of
the initial graph. The finite size scaling properties are then studied numerically in detail in the critical region, and we
propose a consistent set of critical exponents, which does not coincide with the set of standard percolation exponents for
this model. We clarify several aspects in combinatorial optimization and spectral properties of the adjacency matrix of random
graphs.
Received 31 January 2001 and Received in final form 26 June 2001 相似文献
16.
B. Tadić V. Priezzhev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):143-146
We investigate by random-walk simulations and a mean-field theory how growth by biased addition of nodes affects flow of the
current through the emergent conducting graph, representing a digital circuit. In the interior of a large network the voltage
varies with the addition time s < t of the node as V(s) ∼ ln(s)/s
θ when constant current enters the network at last added node t and leaves at the root of the graph which is grounded. The topological closeness of the conduction path and shortest path
through a node suggests that the charged random walk determines these global graph properties by using only local search algorithms. The results agree with mean-field theory on tree structures, while the numerical method is applicable
to graphs of any complexity.
Received 26 August 2002 Published online 29 November 2002 相似文献
17.
V.V. Mourzenko J.-F. Thovert P.M. Adler 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):75-85
Two-scale porous media are generated by filtering a Gaussian random correlated field with a random correlated threshold field.
The percolation threshold and the critical exponent ν are derived with the help of a finite-size scaling method. The percolation
threshold for the three-dimensional media is a decreasing function of the variance and correlation length of the threshold
field. A simplified model predicts these trends in 3d; moreover, it suggested some effects in 2d which were all numerically
verified.
Received 17 August 2000 相似文献
18.
J. Bhattacharya P.P. Kanjilal 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):399-403
The correlation coefficient vs. prediction time profile has been widely used to distinguish chaos from noise. The correlation coefficient remains initially
high, gradually decreasing as prediction time increases for chaos and remains low for all prediction time for noise. We here
show that for some chaotic series with dominant embedded cyclical component(s), when modelled through a newly developed scheme
of periodic decomposition, will yield high correlation coefficient even for long prediction time intervals, thus leading to
a wrong assessment of inherent chaoticity. But if this profile of correlation coefficient vs. prediction horizon is compared with the profile obtained from the surrogate series, correct interpretations about the underlying
dynamics are very much likely.
Received 8 March 1999 相似文献
19.
In this paper we construct networks for music and attempt to compose music artificially. Networks are constructed with nodes and edges corresponding to musical notes and their co-occurring connections. We analyze classical music from Bach, Mozart, Chopin, as well as other types of music such as Chinese pop music. We observe remarkably similar properties in all networks constructed from the selected compositions. We conjecture that preserving the universal network properties is a necessary step in artificial composition of music. Power-law exponents of node degree, node strength and/or edge weight distributions, mean degrees, clustering coefficients, mean geodesic distances, etc. are reported. With the network constructed, music can be composed artificially using a controlled random walk algorithm, which begins with a randomly chosen note and selects the subsequent notes according to a simple set of rules that compares the weights of the edges, weights of the nodes, and/or the degrees of nodes. By generating a large number of compositions, we find that this algorithm generates music which has the necessary qualities to be subjectively judged as appealing. 相似文献
20.
K. Broderix M. Weigt A. Zippelius 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):441-455
We consider the gelation of particles which are permanently connected by random crosslinks, drawn from an ensemble of finite-dimensional
continuum percolation. To average over the randomness, we apply the replica trick, and interpret the replicated and crosslink-averaged
model as an effective molecular fluid. A Mayer-cluster expansion for moments of the local static density fluctuations is set
up. The simplest non-trivial contribution to this series leads back to mean-field theory. The central quantity of mean-field
theory is the distribution of localization lengths, which we compute for all connectivities. The highly crosslinked gel is
characterized by a one-to-one correspondence of connectivity and localization length. Taking into account higher contributions
in the Mayer-cluster expansion, systematic corrections to mean-field can be included. The sol-gel transition shifts to a higher
number of crosslinks per particle, as more compact structures are favored. The critical behavior of the model remains unchanged
as long as finite truncations of the cluster expansion are considered. To complete the picture, we also discuss various geometrical
properties of the crosslink network, e.g. connectivity correlations, and relate the studied crosslink ensemble to a wider class of ensembles, including the Deam-Edwards
distribution.
Received on 24 April 2002 Published online 14 October 2002
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ID="b"e-mail: weigt@theorie.physik.uni-goettingen.de 相似文献